The present invention relates in general to systems and methods for controlling servo-controlled and/or automatic vehicle gearboxes. More specifically, the present invention relates to a control system and a method which can reproduce and optimize She gear-shifting operations of a human driver.
The control strategies of the system have to adapt to the operative conditions of the vehicle in order to maintain the driving sensation required by the user.
In particular, the servo-controlled gearbox must react to the driver""s commands correctly, even during emergency operations, during sports driving and on particularly demanding road sections such as mountain routes.
Automatic and servo-controlled gearboxes according to the prior art in fact have the disadvantage of using different strategies from those which would be adopted by a human driver. This means that the driver of a motor-vehicle having such an automatic gearbox feels uneasy when he is driving and is unsure of the reactions of the gearbox so that driving safety is reduced. The driver""s psychological uneasiness may also reduce has concentration during driving.
A classical example of the problems which may be encountered with the use of conventional automatic gearboxes is the following. Faced with a descent, the driver usually lifts his foot from the accelerator in order to compensate for the effect of gravity which tends to cause the vehicle to accelerate. The automatic gearbox control often interprets this action as an intention by the driver to proceed more economically, that is, as a request for less power/acceleration, and hence engages a higher gear than the previous one. The driver thus loses the engine braking effect on which he was counting to limit the vehicle speed. He is therefore forced to brake or to force the automatic gearbox manually into a lower ratio if he does not wish to use the brakes (or if they are not to be overheated). On a stretch of mountain road, however, this means that driving becomes disagreeable since it requires the driver to override the control system of the automatic gearbox (substituting himself for it) by using it as a manual gear-shift.
U.S. Pat. No. 5,406,483 discloses a system for controlling the transmission in an off-road vehicle having an internal combustion engine and a multiple gear powershift transmission. The system comprises a microprocessor control unit, a plurality of sensors coupled to said control unit for providing signals representative of physical entities relating to the operation of the vehicle, and actuators which are driven by the control unit for controlling the operation of the gearbox. The system is adapted to implement different gearbox control strategies in dependence on the driving conditions detected. Speed selection means allow the user to select a desired vehicle ground speed and the system automatically selects the specific transmission gear and engine speed required to achieve the desired ground speed.
U.S. Pat. No. 5,113,721 discloses a system for controlling a motor vehicle drive train combining an electronic engine power control and an automatic transmission. Movements of an accelerator pedal and a brake pedal are monitored by a computer and predetermined motion sequences are selectively picked up as direct gear selection control instructions.
Other control systems for servo-assisted or robotized gearboxes are disclosed in EP-A-0,695,665 and FR-A-2,732,278.
The object of the present invention is to provide a system and a method for controlling a servo-controlled gearbox which solves all of the problems indicated above in a satisfactory manner.
According to the present invention, this object is achieved by means of a system and a method for controlling a servo-controlled gearbox having the features defined in claims 1 and 13.